1. Field of the Invention
This invention relates generally to a separately power-feeding welding generator, and more particularly to a separately power-feeding welding generator adapted to control the output of at least one of main generating windings by thyristor control to ensure separate power-feeding control.
2. Description of the Prior Art
The present applicant previously proposed in Japanese patent application No. 133930-1984 a separately power-feeding welding generator having main generating windings for a plurality of welding power supplies and adapted to control the output of at least one of the main generating windings by means of thyristor control to ensure separate power-feeding control.
FIG. 4 is a circuit diagram of the welding generator previously proposed by the present applicant. With this circuit configuration, a separately power-feeding welding generator has been realized, in which outputs from a plurality of main generating windings can be independently controlled, and the difference between a current during welding and a current in a shortcircuited state can be reduced without unwantedly reducing no-load current, and the voltage across the output terminals is prevented from being interrupted.
In FIG. 4, a circuit configuration having only one main generating winding and only one rectifying circuit is shown in the interest of simplicity. In addition, a circuit configuration for controlling a thyristor corresponding to the W phase is shown for also simplicity.
With this circuit configuration, however, the following unwanted problems are encountered due to different electrical appliance and material control laws in various countries.
(1) In a dielectric strength test (between the output terminal of the generator and the ground), semi-conductor elements might be damaged because test voltage is applied directly to the thyristor control circuit.
(2) If the voltage applied across the battery terminals becomes excessive (over 20 volts, for example) due to the failure of the regulator (not shown in FIG. 4) for charging the battery (the d-c power supply 15 in FIG. 4) for supplying control voltage to the control circuit, the d-c power supply control circuit 16 shown in FIG. 4 might be adversely affected.
Therefore, a circuit configuration suited to electrical appliance and material control laws in various countries has long been hoped for.